QUINCY -- The city has terminated its land disposition agreement with private developer Street-Works, ending a partnership that had proposed a $1.6 billion revitalization of downtown.

Mayor Thomas Koch on Monday sent a letter to Street-Works partners Ken Narva and Jeffrey Levien telling them he was exercising his right, as written into the 2010 land disposition agreement between the city and developer, to end their partnership because Street-Works failed to meet key project benchmarks by the end of business hours Friday.

Koch had given Street-Works 30 days to submit permitting plans and financial reports – along with approximately $1 million in filing fees – for the first step of the project. Street-Works, which first became interested in Quincy Center redevelopment nearly a decade ago and then officially partnered with the city in 2010, originally proposed bringing 3.5 million square feet of new residential, retail, office, entertainment and educational space to downtown by 2020.

Koch has said he would seek a new development partner, or multiple partners, to pursue downtown redevelopment if the deal with Street-Works had ended.

Quincy Mutual Fire Insurance, one of the two major downtown investors, has said the first block of the project called Merchants Row, expected to bring new residential and retail space to Chestnut Street, Cottage Avenue and the 1400 block of Hancock Street, will go forward as private construction with no city land deal. Work on Merchants Row likely won’t start until spring of 2015 at the earliest, Quincy Mutual has said.

In Koch’s letter to Street-Works on Monday, the mayor said the city would retain all funds that remain in a special consulting account replenished by Street-Works. Last month, the city said the account currently contained $96,750.52.

In addition, Koch said Street-Works is required by the land disposition agreement to turn over all its redevelopment plans to the city, without cost or expense to the city.